马来西亚沙捞越盆地东北部第三系石英表面形态特征--对古沉积环境与储集层质量的指示意义

Quartz surface morphology of Tertiary rocks from North East Sarawak, Malaysia: Implications for paleo-depositional environment and reservoir rock quality predictions

基于马来西亚沙捞越(Sarawak)盆地Belait组和Lambir组第三系露头样品,分析其石英表面形态,揭示其颗粒表面结构缺陷(源自风化作用和成岩作用)、古沉积环境以及储集层质量之间的相关关系。研究利用岩石薄片进行矿物识别,并观察粒径和结构;利用扫描电镜对样品的表面形态进行表征,以展现石英颗粒表面结构的变化。Belait组砾岩的扫描电镜图像表明其以自形石英晶体为主,常见机械风化缺陷,例如线性断口、贝壳状断口以及擦痕;而Lambir组砂岩中却常见化学风化特征,例如化学蚀痕、蚀坑、溶解坑以及刻痕。基于岩石学、扫描电镜以及CT扫描图像分析的储集层质量评价结果表明,研究区Belait组为高能海岸沉积,潮控特征明显,Lambir组为浅海—三角洲沉积,浪控特征明显;Belait组和Lambir组的储集层质量较差,但Belait组的孔隙度略高于Lambir组。

The relationship between quartz surface textural defects（derived from weathering and diagenesis）, palaeo-depositional environment and reservoir quality were studied using Tertiary outcrop rock samples obtained from the Belait and Lambir formations of the Sarawak Basin, Malaysia. Thin sections were used for mineral identification and to make observations regarding grain size and texture. Morphological characterization of the samples was performed using scanning electron microscopy（SEM） attached with energy-dispersive X-ray spectrometry（EDX） system, to show variations in quartz surface texture. The SEM images of Belait conglomerates reveal euhedral quartz crystals characterized with prominent mechanical weathering defects（such as straight and conchoidal fractures and striations）. Conversely, the analysis of the Lambir sandstones identified chemical weathering features（such as chemical etchings, pitting, solution pits and notches）. On the basis of petrology, SEM and CT scan images, evaluation results of reservoir quality indicate that the Lambir Formation in this study area is high-energy coast deposit, with apparent tide-dominated features; while Belait Formation is neritic-delta deposit, with obvious wave-dominated features; reservoir quality of the Belait Formation and Lambir Formation are poor, but the porosity of the Belait Formation is relatively higher than that of the Lambir Formation.